Projected studies will be involved in two general areas: A) Oxygen dependent biosynthetic pathways are threatened by oxygen depletion. Content of oxygen dependent enzymes may be regulated in response to oxygen depletion. We will investigate the effects of pO2 on content, rate of synthesis and rate of degradation of yeast tryptophan oxygenase (such as O2 dependent enzyme). B) Hyperoxic exposure inhibits cell replication and increases cellular cyclic AMP content. We will further explore the possibility that elevated cyclic AMP content mediates inhibition of replication.